At present machines for making filter bags are designed according to various architectures depending on the shape of the filter bag and/or the type of product it contains.
For making traditional type single- or double-chamber, single- or double-lobe filter bags (containing narrow or fine leaf products which can be compacted), machines are usually structured according to a substantially horizontal feed/production line, so that they guarantee high operating speeds and high productivity.
For filter bags which have different geometries, in particular single-chamber with greater three-dimensional dimensions, such as prior art pyramid-shaped filter bags (which may also contain wide or rounded leaf products), machines are used which are structured with a substantially vertical feed/production line, although allowing lower operating speeds and lower productivity.
In machines with a horizontal production line a continuous web of filter paper is fed horizontally along a predetermined path in which the web encounters a series of operating stations designed to allow the production of a continuous tube of filter paper. Said stations include a product filler positioned perpendicularly to the web being fed and designed to deposit a predetermined charge of product with predetermined spacing between each charge on the web. Then there is a series of stations designed to fold the continuous tube, to seal edges of the tube and if necessary to apply a string, tag and outer envelope. Single-chamber, single-lobe filter bags obtained with machines which have a horizontal production line are usually relatively flat, in other words they have reduced three-dimensional dimensions.
With machines using a vertical feed-production axis, on the other hand, it is possible to make pyramid-shaped single-chamber filter bags which have considerable three-dimensional dimensions. Such machines comprise a feed channel extending vertically on which a continuous web of filter paper is wrapped to form a tube, into which the product is made to fall by gravity using screw fillers or revolving fillers. Once filled with product, the tube is intercepted, during tube feed, by a forming and closing station for forming the filter bag into the desired shape and for closing the open edges. Such machines with a vertical feed/production axis for pyramid-shaped single-chamber filter bags have lower operating speeds than machines which have a horizontal feed/production axis for single-chamber, single-lobe filter bags. Usually, machines with a vertical feed/production axis are combined with additional and independent machines (connected to each other by means of suitable conveyor belts) for applying any accessories, such as string, a tag, and if necessary an outer envelope, to the filter bags.
As is briefly illustrated, machines with a horizontal feed/production axis and machines with a vertical feed/production axis have intrinsic features, linked to the operating speeds and the type of filter bag to be made.
At present, there is commercial demand for packaging wide-leaf infusion products in single-chamber, single-lobe filter bags with significant three-dimensional dimensions, for example of the type illustrated in patent applications WO 2008/015509 and WO 2008/152498. Such bags are difficult to make on machines with horizontal feed. This is because in such machines the filter paper has reached extremely high speeds and accelerations and placing the charges of product on the filter paper web is a problem.
The speed and accelerations which would be applied to the charges of wide-leaf product (often having rounded edges) uncompacted and deposited on the filter paper web, would result in product movements on the web, with respective breaking up of the charge. That would cause a low end quality of the filter bag, for example different quantities of charge in each filter bag made, or product trapped in the seals on the edges.
Therefore, obviously, in order to be able to use this type of product on machines with horizontal feed the operating speed would have to be reduced to the detriment of productivity in the unit of time, causing a reduction in the real capacity of the machine, but without even providing the certainty of a good result on the finished product.
Moreover, as already indicated, prior art machines with a horizontal production line do not allow single-chamber, single-lobe bags with significant three-dimensional dimensions to be made.
Machines with feed/production along the vertical axis have the problem already indicated, of operating speed and productivity which are lower than those of horizontal type machines. This is mainly due to the filling system and the consequent structuring of the machine in its entirety.
Filling is performed using gravity along the vertical axis and using, for example, screw feeder or revolver systems. Therefore, filling requires relatively long times correlated with the speed of the systems, the drop time for the product to be filled and the distance between the filler and the subsequent stations for handling the filter bags.
Moreover, machines of the type just described are extremely bulky.
In addition, as already indicated, this type of structure means that these machines must be connected to a second machine which allows the application of additional elements to the filter bag with respective release/conveyor/pickup systems present between the two machines.